1. Field of the Invention
The present invention relates to a pump unit that is operatively connected to a driving source and fluidly connected to an actuator via a hydraulic circuit so as to be capable of outputting driving power with variable speed through the actuator.
2. Background Art
The hydraulic pump unit is used in various fields of applications, one of which is directed to a cooperative operation with the actuator which is arranged away from the hydraulic pump unit. In this application, the hydraulic pump unit and the actuator are connected to each other via a hydraulic circuit so as to together constitute a main transmission path for receiving driving power from a driving source and outputting the same with variable speed.
In some applications, a power transmission structure equipped with the hydraulic pump unit requires a sub transmission path in addition to the main transmission path. Such a requirement exists, for example, in a lawn mower, in which power from a common driving source is divided and output into a running-power transmission path and a PTO power transmission path.
Now, the description will be made for the arrangement where a hydraulic motor unit is used as the actuator.
U.S. Pat. Nos. 4,395,865 (hereinafter referred to '865 patent), 5,809,756 (hereinafter referred to '756 patent) and other prior art references disclose a lawn mower that includes a PTO power transmission path for receiving power from an engine and outputting the same to a mower as well as a running power transmission path that is made up of a hydraulic pump unit operatively connected to the engine and a hydraulic motor unit located away from the hydraulic pump unit so as to drive driving wheels.
Specifically, the lawn mower in the '865 patent provides the engine as a common driving source with first and second output shafts, which are respectively and operatively connected to the hydraulic pump unit and a mower unit. That is, in the lawn mower of the '865 patent, the running power transmission path is entirely separated from the PTO power transmission path. However, this entire separation of the running power transmission path and the PTO power transmission path necessitates a large number of parts for separately forming these transmission paths and a large space for accommodating these separate transmission paths. Also, the power transmission structure with two separate power transmission paths requires independent control for enabling and disabling the transmission of power in each transmission path. In order to achieve this control, in the lawn mower of the '865 patent, an electromagnetic clutch for enabling and disabling the transmission of power is placed in each transmission path. This electromagnetic clutch has however poor durability, and therefore may result in loss in reliability to each transmission path.
On the other hand, the lawn mower of the '756 patent provides the engine with a common output shaft, on which a driving pulley and a mower pulley are supported, so that power can be divided into the running power transmission path and the PTO power transmission shaft through this common output shaft. In order to achieve this arrangement, the common output shaft must be lengthened, which results in a larger load applied thereon. The '756 patent is also silent as to how to enable and disable the transmission of power in each transmission path.
The present invention has been conceived in consideration of the above prior arts. Accordingly, it is an object of the present invention to provide a pump unit that is operatively connected to a driving source and fluidly connected to an actuator via a hydraulic circuit so as to output driving power with variable speed through the actuator, and has a simplified structure enabling dividing driving power from the driving source into a sub transmission path as well as into a main transmission path, which the pump unit constitutes in cooperation with the actuator.
It is another object of the present invention to provide a working vehicle having a simplified structure, which includes a PTO power transmission path extending from a drive source to a working unit for land treatment such as a mower unit (hereinafter simply referred to as “working unit”), as well as a running power transmission path that is made up of a hydraulic pump unit for receiving driving power from a driving source, and a hydraulic motor unit located away from the hydraulic pump unit and fluidly connected thereto.